The long term goal of this research is to develop low cost and accurate methods for regional flow measurements in tissues. This research is based on the working hypothesis that fluorescent microspheres in tissue digests can be accurately and rapidly counted in a fluorescence flow system. The project will develop instrumentation and evaluate procedures to count microspheres in tissue digests. During Phase I a continuous flow fluorescent microsphere counting system will be assembled and conditions for the accurate counting of microspheres determined. Time profiles of microsphere passage will be evaluated and results compared with the fluorescence spectrophotometry method. Phase I studies will demonstrate the feasibility of the working hypothesis and provide design parameters for automated systems to be constructed during Phase H for testing in physiology research environments to evaluate its utility and ease of use. This project will provide researchers with a valuable tool for lowering the cost and labor involved in regional flow measurements and improve the attraction of using fluorescent microspheres to replace the older radioactive microsphere methods. PROPOSED COMMERCIAL APPLICATION: This technology would replace current methods for estimating numbers of microspheres with a potentially more accurate method that has lower capital, supplies, and labor costs. Potential markets include the hundreds of laboratories currently using fluorescent microspheres and the large number of additional researchers utilizing the alternative radioactive and colored microsphere methods.